U.S. patent number 5,979,270 [Application Number 09/112,363] was granted by the patent office on 1999-11-09 for hydrostatic transaxle.
This patent grant is currently assigned to Unipat AG. Invention is credited to George Duncan McRae Arnold, Christian Helmut Thoma.
United States Patent |
5,979,270 |
Thoma , et al. |
November 9, 1999 |
**Please see images for:
( Certificate of Correction ) ** |
Hydrostatic transaxle
Abstract
A hydrostatic transaxle axle assembly for a vehicle such as a
grass mowing lawn or garden tractor comprising a housing for an
internally disposed hydrostatic transmission having a
variable-displacement hydraulic pump fluidly connected to a
fixed-displacement hydraulic motor, the hydraulic motor being
connected by differential gearing to axle shafts supported in the
housing. The housing is formed by three housing members, two of
which are preferably separable on a parting plane coincident with
the longitudinal axes of the axle shafts. One of the housing
members being provided with an opening to allow a portion of one of
the other housing members to extend through, and where the
extending housing member contains within its interior a number of
internal fluid passages for fluidly connecting the hydraulic pump
to the hydraulic motor. This construction allows for improved
cooling of the power transmitting fluid flowing between the pump
and motor and simplifies manufacture of the transaxle such that the
bulk or all the machining operations can be carried out in only one
of the three housing elements, this housing member being the
smallest of the three which can be completed using a comparatively
smaller sized CNC machining-center than would otherwise be the
case. The two remaining housing elements may be used in an as cast
or supplied condition.
Inventors: |
Thoma; Christian Helmut
(Jersey, GB), Arnold; George Duncan McRae (Jersey,
GB) |
Assignee: |
Unipat AG (Glarus,
CH)
|
Family
ID: |
26730043 |
Appl.
No.: |
09/112,363 |
Filed: |
July 9, 1998 |
Current U.S.
Class: |
74/606R; 475/83;
60/487 |
Current CPC
Class: |
B60K
11/06 (20130101); B60K 17/105 (20130101); Y10T
74/2186 (20150115); F16H 57/02 (20130101); B60Y
2200/223 (20130101) |
Current International
Class: |
B60K
11/06 (20060101); B60K 17/10 (20060101); B60K
11/00 (20060101); F16H 57/02 (20060101); F16H
057/02 () |
Field of
Search: |
;174/66R ;475/83,84
;60/487,464 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Wright; Dirk
Assistant Examiner: Kwon; Peter T.
Attorney, Agent or Firm: Young & Thompson
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATION
This application claims the benefit under 35 USC .sctn.119(e) of
provisional application No. 60/051,990 filed Jul. 9, 1997.
Claims
We claim:
1. An axle assembly comprising a housing having an internal chamber
for an internally disposed hydrostatic transmission and forming an
integral part of said hydrostatic transmission, said hydrostatic
transmission comprising a variable-displacement hydraulic pump and
a fixed-displacement hydraulic motor; axle shafts rotatably
supported in said housing and differential gearing means supported
by said housing drivingly connected between said hydraulic motor
and said axle shafts, said housing comprising first, second and
third housing members and where said first and second housing
members are joined together on a first parting plane and where said
second and third housing members are joined on a second parting
plane and wherein said first housing member includes internal fluid
passages arranged to fluidly connect said hydraulic pump to said
hydraulic motor.
2. An axle assembly according to claim 1 wherein the longitudinal
axis of said axle shafts is substantially coincident with said
second parting plane and offset from said first parting plane.
3. An axle assembly according to claim 1 wherein the longitudinal
axis of said axle shafts is parallel to said second parting plane
and offset from said first parting plane.
4. An axle assembly according to claim 1 wherein the axis of
rotation of said hydraulic pump is perpendicular to the first and
second parting planes, and where the axis of rotation of said
hydraulic motor is substantially coincident with said second
parting plane and parallel and offset from said first parting
plane.
5. An axle assembly according to claim 1 wherein said first housing
member provides first and second fluid coupling surfaces for said
hydraulic pump and said hydraulic motor respectively, bearing means
provided in said first housing member for the support of an input
drive shaft and where a cylinder-barrel containing a plurality of
pistons of said hydraulic pump is arranged to be driven by said
input drive-shaft and operatively connected to the first fluid
coupling surface, said internal fluid passages within said first
housing element connecting first and second fluid coupling surfaces
together and where the second fluid coupling surface is operatively
connected to a further cylinder-barrel acting as a component of
said hydraulic motor.
6. An axle assembly according to claim 1 wherein bearing means are
provided in said first housing member for the support of an input
drive shaft and where a cylinder-barrel containing a plurality of
pistons of said hydraulic pump is arranged to be driven by said
input drive-shaft, said internal fluid passages within said first
housing element connecting with said hydraulic pump, the relative
positions of said bearing means and said internal fluid passages
being such that said internal fluid passages are positioned nearer
to said second parting plane.
7. An axle assembly according to claim 6 wherein further bearing
means are provided in said third housing member to support said
input drive-shaft.
8. An axle assembly according to claim 6 wherein further bearing
means are provided in said first housing member to support the
drive-shaft of said hydraulic motor.
9. An axle assembly according to claim 5 wherein said hydraulic
pump is of the axial piston swash plate type and where said smash
plate is positioned adjacent to said third housing member and
supported by means of a support surface located in said third
housing member.
10. An axle assembly according to claim 9 wherein a vent valve is
included within said first housing member, said vent valve when
fully activated causing said internal fluid passages within said
first housing member to short-circuit thereby interrupting the
fluid connection between said hydraulic pump and said hydraulic
motor.
11. An axle assembly according to claim 10 wherein a control shaft
is supported in said first housing member and is operatively
connected to said variable displacement hydraulic pump, said
control shaft being operatively connected to said vent valve for an
enhanced wide-band neutral effect for said hydrostatic
transmission.
12. An axle assembly according to claim 5 wherein a cooling fan
driven by said input drive shaft provides means for cooling the
upper surface of said first housing member and where said internal
fluid passages are in spaced relationship to said upper
surface.
13. An axle assembly according to claim 5 wherein said internal
fluid passages are in spaced relationship to the exterior surface
of said first housing member and where an input shaft driven fan
operating above and cooling the exterior surface of said first
housing member provides means for controlling the temperature of
the fluid flowing between said hydraulic pump and said hydraulic
motor.
14. An axle assembly according to claim 1 wherein said first
parting plane is arranged to be on the upper exterior surface of
said second housing member and where a portion of said first
housing element extends through an opening provided in said second
housing member to protrude into said internal chamber.
15. An axle assembly according to claim 1 wherein said first
parting plane is arranged to be on the lower interior surface of
said second housing member and where a portion of said first
housing element extends through an opening provided in said second
housing member to protrude above the exterior upper surface of said
second housing member.
16. An axle assembly comprising a housing having an internal
chamber for an internally disposed hydrostatic transmission and
forming an integral part of said hydrostatic transmission, said
hydrostatic transmission comprising a variable-displacement
hydraulic pump and a fixed-displacement hydraulic motor; outwardly
extending axle shafts rotatably supported in said housing and
differential gearing means supported by said housing drivingly
connected between said hydraulic motor and said axle shafts; said
housing being defined by three housing members and where two of
said housing members are separable at a parting plane generally
containing the longitudinal axes of said axle shafts; and where an
opening is provided in one of said housing members to allow a
portion of the remaining housing member to extend through and where
that housing member having the extending portion contains within it
internal fluid passages arranged for fluidly connecting said
hydraulic pump to said hydraulic motor.
17. An axle assembly according to claim 16 wherein that said
housing member having the extending portion is provided with first
and second fluid coupling surfaces for said hydraulic pump and said
hydraulic motor respectively, bearing means provided in that said
housing member having the extending portion for the support of an
input drive shaft and where a cylinder-barrel containing a
plurality of pistons of said hydraulic pump is arranged to be
driven by said input drive-shaft and operatively connected to the
first fluid coupling surface, said internal fluid passages
connecting first and second fluid coupling surfaces together and
where the second fluid coupling surface is operatively connected to
a further cylinder-barrel acting as a component of said hydraulic
motor.
18. An axle assembly according to claim 17 wherein a cooling fan
driven by said input drive shaft provides means for cooling the
upper surface of that said housing member having the extending
portion and where said internal fluid passages are in spaced
relationship to said upper surface.
19. An axle assembly according to claim 17 wherein said internal
fluid passages are in spaced relationship to the exterior surface
of that said housing member having the extending portion and where
an input shaft driven fan operating above and cooling the exterior
surface of that said housing member having the extending portion
provides means for controlling the temperature of the fluid flowing
between said hydraulic pump and said hydraulic motor.
20. An axle assembly comprising a housing having an internal
chamber for an internally disposed hydrostatic transmission and
forming an integral part of said hydrostatic transmission, said
hydrostatic transmission comprising a variable-displacement
hydraulic pump and a fixed-displacement hydraulic motor; an
outwardly extending axle shaft rotatably supported in said housing
and gearing means supported by said housing drivingly connected
between said hydraulic motor and said axle shaft; said housing
being defined by three housing members and where two of said
housing members are separable at a parting plane generally
containing the longitudinal axis of said axle shaft; and where an
opening is provided in one of the said housing members to allow a
portion of one of the other housing members to extend through and
where that housing member having the extending portion contains
within it internal fluid passages arranged for fluidly connecting
said hydraulic pump to said hydraulic motor.
21. An axle assembly according to claim 20 wherein that said
housing member having the extending portion is provided with first
and second fluid coupling surfaces for said hydraulic pump and said
hydraulic motor respectively, bearing means provided in that said
housing member having the extending portion for the support of an
input drive shaft and where a cylinder-barrel containing a
plurality of pistons of said hydraulic pump is arranged to be
driven by said input drive-shaft and operatively connected to the
first fluid coupling surface, said internal fluid passages
connecting first and second fluid coupling surfaces together and
where the second fluid coupling surface is operatively connected to
a further cylinder-barrel acting as a component of said hydraulic
motor.
22. An axle assembly according to claim 20 wherein a cooling fan
driven by said input drive shaft provides means for cooling the
upper surface of that said housing member having the extending
portion and where said internal fluid passages are in spaced
relationship to said upper surface.
23. An axle assembly according to claim 20 wherein said internal
fluid passages are in spaced relationship to the exterior surface
of that said housing member having the extending portion and where
an input shaft driven fan operating above and cooling the exterior
surface of that said housing member having the extending portion to
provides means for controlling the temperature of the fluid flowing
between said hydraulic pump and said hydraulic motor.
24. An axle assembly comprising a housing having an internal
chamber for an internally disposed hydrostatic transmission and
forming an integral part of said hydrostatic transmission, said
hydrostatic transmission comprising a variable-displacement
hydraulic pump and a fixed-displacement hydraulic motor; axle
shafts rotatably supported in said housing and differential gearing
means supported by said housing drivingly connected between said
hydraulic motor and said axle shafts; said housing including a
portion formed with fluid passages disposed within its interior and
arranged to fluidly connect said hydraulic pump to said hydraulic
motor and where an input shaft driven fan operating above and
cooling the exterior surface of said portion provides means for
controlling the temperature of the fluid flowing between said pump
and said motor.
25. An axle assembly according to claim 24 wherein said housing
provides first and second fluid coupling surfaces for said
hydraulic pump and said hydraulic motor respectively, at least one
bearing provided in said housing for the support of an input drive
shaft and where a cylinder-barrel containing a plurality of pistons
of said hydraulic pump is arranged to be driven by said input
drive-shaft and operatively connected to the first fluid coupling
surface, said internal fluid passages within said housing
connecting first and second fluid coupling surfaces together and
where the second fluid coupling surface is operatively connected to
a further cylinder-barrel acting as a component of said hydraulic
motor.
Description
FIELD OF THE INVENTION
This invention relates to hydrostatic transaxles, and more
particularly, to a compact, fully integrated hydrostatic transaxle
incorporating a hydrostatic transmission of the type employing an
axial piston swash-plate pump and hydraulic motor.
Hydrostatic-transmissions in association with transaxle driving
apparatus have proven to be very useful to-date and are used in
numerous applications such as small vehicles like self-propelled
grass-mowing lawn tractors.
BACKGROUND OF THE INVENTION
Hydrostatically powered driven equipment such as lawn tractors have
become extremely popular and many utilise the axial piston
swash-plate configuration for both the pump and motor elements of
the hydrostatic transmission. Such tractors generally have an
internal combustion engine having a vertical crankshaft which is
connected to the transaxle by means of a conventional belt and
pulley arrangement. A standard hydrostatic transmission for such a
transaxle includes a hydraulic pump, which is driven by an input
shaft from the engine output by means of the belt and pulley
arrangement, and a hydraulic motor, both pump and motor are mounted
on a center section located inside the transaxle housing. Rotation
of the pump by an input shaft creates axial motion of the pump
pistons during periods when the pistons are operating against an
inclined thrust or swash-plate. The fluid flow thus created by the
reciprocating axial motion of the pistons is channelled via porting
and passages in the center section to the hydraulic motor, with the
effect that the incoming fluid causes the pistons of the motor to
reciprocate and create a turning moment that causes rotation of the
hydraulic motor. The hydraulic motor in turn has an output shaft
which drives the vehicle's axles through speed-reducing gears and a
mechanical differential. Examples of such hydrostatic transaxles
are shown in the following patents: U.S. Pat. No. 5,090,949; U.S.
Pat. No. 5,473,964 and U.S. Pat. No. 5,501,640.
All three references use an axial piston swash-plate pump and motor
respectively engaged to a center section which is located within a
two-shell housing structure. The main purpose of the center section
is to provide a fluid link between the pump and the motor and
allowing the transmission of hydraulic power. Patents '964 and '640
in the names of Okada and Hauser respectively, teach the use of an
input shaft driven pump where the swash-plate lies adjacent to the
upper housing. This contrasts with the disclosure in patent '949
which teaches the use of bevel gears for connecting the input-shaft
to the pump and where in this example of prior art, the swash-plate
of the pump lies directly across both the upper and lower housings
of the transaxle.
The center section shown in all three above references require
numerous machining operations to prepare the initial raw casting to
be ready for use. For instance: drilling some or all of the
internal flow passages and arranging retaining means so that
plugs/valves and such like can be subsequently fitted to close off
the flow circuit; making good two of the faces which provide the
fluid coupling means for the pump and motor, and when required, for
the subsequent attachment of the valve-plates; preparation of
mounting surfaces for attaching the center section to the housing
structure. Furthermore, the upper transaxle housing aluminum
diecasting itself requires a number of machining operations before
it can be used such as the provision for the shaft bearing and seal
as well as hole or holes and seals for the control lever and
various associated linkages.
As a general rule, the more machining operations required in the
upper transaxle housing casting as well as the more complex
operations required in the center section casting, the greater the
cost of manufacture of the complete hydrostatic transaxle.
Therefore the reduction in the number of such machining operations
and by grouping them into one rather than two components would save
expense.
Although only shown in the '949 patent, almost all hydrostatic
transaxles make use of a cooling fan mounted to the input drive
shaft in an attempt to help prevent the internal components and
fluid from overheating. However, the prior art teaches a center
section which although attached in some manner to the interior of
the housing, it is still essentially a separate entity from the
transaxle housing. As a result, effective cooling of the fluid
passing through the passages in the center section that connect the
pump and motor together is hindered as the fluid surrounding the
center section acts as a insulator to slow down the rate of heat
transfer from the power transmission fluid in said passages to the
surrounding housing radiator.
The amount of heat able to be radiated away from the transaxle
housing exterior to the surrounding environment is of course
greatly enhanced over that region on the boundary of the transaxle
housing that lies directly in the path of the air flow from the
cooling fan. However, it is apparent that although the fluid inside
the housing nearest that region where the fan is operating is being
cooled, fluid elsewhere may still remain at very high temperature.
Perhaps more importantly, as the fluid circulating between the pump
and motor in the fluid passages in the center section becomes
extremely hot during operation, especially when the unit is heavily
loaded and used in a high ambient temperature environment, the
resulting drop of operating efficiency due to decreasing fluid
viscosity and a corresponding increase in fluid leakage losses can
be a concern with the prior art.
This problem exists because the attendant power losses associated
with such close coupled pump and motor combinations produce a lot
of unwanted heat due to the rapid fluid compression/decompression
cycles and general friction between the sliding surfaces. Such
losses causes the fluid circulating between the pump and motor
through the center section to become extremely hot, and because the
prior art teaches a transaxle housing structure whereby the
internal fluid reservoir completely or almost completely surrounds
and insulates the center section, these prior solutions are not
conducive to the promotion of most effective cooling for the
circulating fluid in the centre section flowing in a closed-loop
circuit between the pump and motor. This limitation occurs because
the bulk of the heat accumulating in the center section can only be
transferred by conduction to the surrounding hydraulic fluid and
then through the fluid itself to reach the boundary walls of the
housing surrounding the fluid chamber from where it can be radiated
away to the surroundings. The remove of unwanted heat from the
center section consequently takes time.
Therefore in these prior devices where the center section is
effectively insulated by the surrounding hydraulic fluid, the delay
in the transfer of unwanted heat out of the transaxle may on
occasion result in the fluid of the hydrostatic transmission
becoming overheated with the risk that the operational life of the
fluid tis shortened or that the lubricating properties of the fluid
deteriorates to the extent that threatens the useful operational
life of then hydrostatic transaxle.
SUMMARY OF THE INVENTION
An object of the invention is to eliminate the need to use a
conventional centre section in the hydrostatic transaxle
product.
A further object of the invention is to provide a hydrostatic
transaxle in which most or all the machining can be carried out in
one housing member compared to the prior art where such operations
need to be carried out in both the housing as well as the center
section.
A still further object of the invention is the grouping of the
fluid coupling surfaces for the pump and motor as well as the heat
dissipating means on the exterior surfaces on a single housing
component, including fluid passages arranged in its interior with
bearings, seals, control shafts supported in machined pockets.
A further object of the invention is to improve the cooling of the
operating fluid circulating between the pump and motor. With this
invention, fan cooling of the housing very effective in lowering
the temperature of the hydrostatic transmission fluid as it
circulates in the closed-loop circuit between the pump and motor as
much of the heat is conducted directly into the material of the
housing in the area directly under the path of the air from the
cooling fan.
What is needed in the art is a compact hydrostatic transaxle for
vertical input shaft installations where the amount of machining
needed to be carried out is consigned to one rather than two or
three main component members, preferable in a manner that would
allow both the upper and the lower transaxle housing elements or
shells for the hydrostatic transaxle to be used in an as cast or
supplied state. What is further needed in the art is improved
cooling for such devices allowing an extension in the operation
duty cycle.
In one form thereof, the hydrostatic transaxle of the invention
comprises an axle assembly with a housing having an internal
chamber for an internally disposed hydrostatic transmission and
forming an integral part of said hydrostatic transmission, said
hydrostatic transmission comprising a variable-displacement
hydraulic pump and a fixed-displacement hydraulic motor; axle
shafts rotatably supported in said housing and differential gearing
means supported by said housing drivingly connected between said
hydraulic motor and said axle shafts; said housing Comprising
first, second and third housing members and where said first and
second housing members are joined together on a first parting plane
and where said second ad third housing members are joined on a
second parting plane and wherein said first housing member includes
internal fluid passages arranged to fluidly connect said hydraulic
pump to said hydraulic motor.
The above mentioned and other novel features and objects of the
invention, and the manner of attaining them, may be performed in
various ways and will now be described by way of examples with
reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an external view from one side of the hydrostatic
transaxle according to the invention.
FIG. 2 is a plan view of the hydrostatic transaxle of FIG. 1 along
the section line I--I.
FIG. 3 is a sectioned view on line II--II of FIG. 2 showing the
hydrostatic transmission.
FIG. 4 is a further sectioned view on line III--III of FIG. 2.
FIG. 5 is a view of an alternative housing construction for the
hydrostatic transaxle of FIG. 1.
FIG. 6 is a part sectional view along line IV--IV of FIG. 5.
FIG. 7 depicts external control linkages for use with the
alternative housing construction of FIG. 5.
FIG. 8 is a part sectional view along line V--V of FIG. 7.
FIG. 9 is a sectioned view taken at line VI--VI of FIG. 8.
FIG. 10 depict various forms of fluid valves for use in the
alternative housing construction.
DETAILED DESCRIPTION OF THE FIRST EMBODIMENT OF THE INVENTION
The first embodiment shown in FIGS. 1 to 4, the outer housing
structure of the hydrostatic transaxle depicted by arrow 1 is
partially defined by an upper transaxle housing element 2 and a
lower transaxle housing element 3 which are joined together at a
junction surface arranged preferably such that the parting-plane 5
is coincident with the output axle shafts 7, 8. Parting-plane can
be called the first parting-plane in this invention. A liquid
gasket seal is applied to the junction surface at the parting plane
5 prior to the two transaxle housings element 2, 3 being secured
together by a plurality of bolts or screws 10. As shown in FIGS. 3
& 4, upper transaxle housing element 2 is arranged to have
opening 12 through which housing member 13 passes and which is then
secured in-place by a plurality of fastening screws 15. A seal ring
or liquid gasket seal is applied to the junction surface 16 between
housings members 2, 13 next to opening 12. Junction surface 16 can
be called the second parting-plane in this invention. All three
housing members 2, 3, 13 when attached together form the
surrounding boundary for an internal chamber 17. Within internal
chamber 17, internal elements of the hydrostatic transaxle are
located therein such as the hydraulic pump, hydraulic motor, speed
reducing gears and mechanical differential. Although internal
chamber 17 may be divided into separate chambers for purposes of
segregating the hydrostatic transmission from the mechanical
gearing (and when required a mechanical differential), the
embodiment hers illustrates the use of a common chamber 17 for all
such components.
Housing member 13 may preferably be cast as one-piece in either
aluminum alloy or iron/steel. If the piece is cast as a pressure
diecasting, many features can be detailed with sufficient accuracy
such that many secondary machining operations can be thus
avoided.
As a portion of housing member 13 containing within it the fluid
passages connecting the pump and motor is exposed to the outer
environment, porosity in the casting could led to fluid leakage.
However, the possibility of such fluid seepage through the material
of the housing member in the present invention can be easily
overcome in at least one way, for instance, through the
impregnating of that portion of the housing member that would
protrude through the opening in the upper housing member of the
transaxle with a resin that prevents leakage occurring.
Housing member 13 contains within its structure fluid passages 20,
21, 22, 23 that connect together the respective fluid coupling
surfaces otherwise known as valve-faces, between the pump and
motor. Fluid passages 20, 21, 22, 23 may be cored in the housing
casting 13 or machined. Plugs 25 are used to blank off the ends of
passages 20, 21. Although in practice it has been known to cast
valve faces in aluminum alloy to provide a running surface for a
cylinder-barrel, most common practice these days is to mount
separate valve-plates on which respective cylinder-barrels can run
against. Most often, such separate valve-plates are surface
hardened so that the sealing surfaces may operate for many
thousands of hours without suffering from undue wear that would
result in a loss in volumetric efficiency of the hydrostatic unit.
In this respect, the faces shown as 28, 29 on the housing member 13
may be cast with countersunk register shown as 30, 31 respectively,
into which respective valve plates 33, 34 are located. However, the
invention would permit the valve faces to be detailed and formed
directly on the surface of the subsidiary housing 13 if
desired.
Check-valves are included in both respective pairs of passages 20,
22 and 21, 23 to allow the admittance of make-up-fluid in order
that the hydrostatic transmissions can recover any fluid loss
during operation because of leakage. In the present invention, the
check-valves shown as 37 have been placed near the lowest position
in the downwardly extending portion shown as 40 of the housing
member 13 such that balls 42 of the check-valves 37 can fall onto
their respective seats 44 by the influence of gravity when not
activated by suction pressure. Although not shown, the linkage
connecting the swash-plate of the pump to the externally protruding
control-lever of the hydrostatic transaxle may be arranged so that
when the pump is at or near neutral, the linkage can act in a
manner to off seat the balls, thereby proving the hydrostatic
transmission with a more positive neutral point.
The respective cylinder-barrels 60, 61 of the
hydrostatic-transmission pump and motor are mounted perpendicular
to one another such that the rotating axis of the pump
cylinder-barrel 60 is vertical and arranged parallel and co-axial
with respect to the input-drive shaft 62 whereas the rotating axis
of the motor cylinder-barrel 61 is parallel with respect to the
rotating axis of the axle-shafts 7, 8. The input drive shaft 62 is
supported by a bearing 63 in the housing element 13 and a seal 64
is used to prevent fluid in the internal chamber 17 from escaping.
Shaft 62 extends downwards and is provided with a spline 65 which
connects with the pump cylinder-barrel 60. Shaft 62 extends further
and passes through the center of the swash-plate 70 to be further
supported by means of a bearing 72 in lower housing member 3.
Bearing 72 is supported in blind hole 71 which ideally may be sized
by the die-caster thereby eliminating any need to machine lower
housing member by the transaxle builder although in practice.
Alternatively, hole 71 could be cast as a through hole and in this
case, an extra seal would then be needed. Bearing 72 may be of the
self-aligning type in which case a plain journal bearing may be
added to the design positioned, this bearing being positioned just
adjacent to valve-plate 33 to act between bearings 63, 72 for
providing additional support for drive-shaft 62.
To overcome any misalignment between the bearing 63 in housing
member 13 and bearing 72 in the lower housing member 3, it is
proposed that during assembly of the hydrostatic transaxle, housing
member 13 is only loosely attached by screws 15 until all the
components have been assembled in place. Then once input shaft 62
is located into bearing 72, this essentially controls the true
position of the housing 13 relative to housing members 2, 3 as the
bearing 63 supported input shaft 62 is thereby in correct alignment
with bearings 72. At that time, screws 15 can be tightened so that
housing elements 2, 13 are thereby locked together.
The cylinder-barrel 60 of the pump is provided with a plurality of
axial cylinder-bores 75, each bore 75 containing a respective
piston 76 and where each piston 76 is being axially urged outwards
by a spring (not shown) located behind the piston 76 in the bore
75. The outer end of the piston 76 is generally domed-shaped to be
operatively connected to an adjacent operating surface 80 of
swash-plate 70 by the bias produced by springs. The action of the
springs behind each of the pistons 76 produces a counter reaction
which loads the cylinder-barrel 60 against the operating surface 81
of the adjacent valve-plate 33. Each cylinder-bore 75 has a port 77
so arranged to communicate in sequence with a pair of
arcuate-shaped ports (although not visible they are identical to
those arcuate-shaped ports 98, 99 shown for the motor) provided on
the valve-plate 33, and where such arcuate-shaped ports are in
fluid connection with fluid passages 20, 21 in housing member
13.
Swash-plate 70 is so arranged for the pump that its inclination
angle can be varied in both directions from its neutral or
zero-inclination point. The swash-plate 70 is seated on a
part-cylindrical bearing 88 provided in the interior of the lower
housing member 3, and connected by linkages (not shown) to a
control-shaft 90 which protrudes from housing member 2 as shown in
FIG. 1. Rotary movement of the control-shaft 90 causes the
swash-plate 70 to incline in angle in respect of the stroking axis
of the pistons 76, and thereby the stroke of the pistons 76 is
changed. The amount of piston 76 stroke determines the amount of
fluid displaced in the cylinder-bore 75 per each single rotation of
the cylinder-barrel 60, and hence the swept volume of the pump can
be changed by altering the amount of piston stroke so that the
amount of fluid delivered to the hydraulic motor is precisely
controlled.
The cylinder-barrel 61 of the motor is almost in all respects
identical to that of the pump, and carries a series of pistons 93
which are operatively connected to the operational surface 94 of
thrust plate 95. Each piston 93 is housed in its respective
cylinder-bore 96 provided within cylinder-barrel 61, and arranged
so that each cylinder-bore 96 can communicate in sequence with
respective arcuate-shaped ports shown as 98, 99 provided in the
valve-plate 34 by means of its respective port 97. Fluid passages
22, 23 in the housing member 13 are arranged to be in fluid
connection with respective arcuate shaped ports 98, 99 in the
valve-plate 34 of the motor by means of respective linking ducts
91, 92. Although not shown, a spring is positioned within each of
the cylinder-bores 96 to engage with its respective piston.
In the case of the motor, the thrust-plate 95 is depicted in its
most often used position which is permanently inclined with respect
of the axis of pistons 93. The thrust-plate 95 is supported on a
insert 100 that is held to the housing member 2, 3 either by
fastening means such as screws or preferably by being pinched tight
between adjacent walls as shown 101, 102 in housing member 2, 3.
Because the inclination angle of the thrust-plate 95 always remains
at an angle during the operation of the device, the piston 93
stroke in the motor remain constant. As the fluid received from the
pistons 76 of the pump can be changed by the action of using
control-shaft 90, the rotation-of the motor can be in either
direction. The cylinder-barrel 61 is mechanically engaged by spline
105 to shaft 106 and thus rotation of the cylinder-barrel 61 causes
rotation of shaft 106. As fluid enters the motor from the arcuate
shaped ports 98, 99 in the valve-plate 34, the fluid entering the
cylinders of the pistons 93 causes the pistons 93 to move axially
outwards and because the reaction on the thrust-plate 95 to the
piston movement is not co-axial with the longitudinal axis of the
pistons 93, an angular driving moment is created on the
cylinder-barrel 61 which is caused to revolve. Therefore rotation
of the cylinder-barrel 61 and shaft 106 is transmitted through the
speed reducing gears to the differential and axle output shafts 7,
8 of the hydrostatic transaxle 1 which in the case of a vehicle
application such as a lawn tractor, are attached the drive wheels
of the vehicle.
Shaft 106 is supported by bearings 110, 111, bearing 110 being
located in the downwards extending portion 40 of subsidiary housing
member 13, whereas bearing 111 is located in a pocket 112 arranged
between housing member 2, 3. The shaft 106 may protrude from the
transaxle so that a conventional disc parking brake can be
attached. A seal 114 is also provided to surround the shaft 106 in
order to prevents fluid seeping out of the internal chamber 17.
A gear 120 fixed to shaft 106 is in mesh with gear 123 which is
fixed to intermediary-shaft 125. Intermediary shaft 125 is
supported by bearings 127, 128 in similar manner to that described
for the shaft 106. Gear 130 fixed to intermediary-shaft 125 is in
mesh with the ring-gear 131 of the differential-assembly.
The ring-gear 131 of the differential-assembly has bevel gears
shown as 132, 133, 134, 135 so that power can be transmitted from
the differential-assembly to the axle-shafts 7, 8 of the transaxle
1 as known to those skilled in the art. The inclusion of a
differential assembly is important as it allows normal
differentiation between the left and right drive wheels of the
vehicle and helps prevent lawn damage especially when tight turns
are undertaken. However, there are applications where no such
differentialled action is required, and in these instances, a
single axle shaft may be used instead of the two as shown in this
embodiment. In the case of a single axle shaft, this shaft can be
arranged to extend outwardly on one or both sides from the
housing.
By means of appropriate selection or adjustment of the inclination
of the swash-plate 70 of the pump by means of the control-shaft 90
and the intermediary linkage, the hydrostatic transmission ratio is
altered. Rotation of the input-shaft 62 causes cylinder-barrel 60
to rotate and results in reciprocation of pistons 76. Fluid is then
delivered from passages 20, 22 or 21, 23 (depending on which
direction of flow occurs from the pump) in the housing member 13
and enters the cylinder-barrel 61 of the motor and causes the
pistons 93 to reciprocate in their respective bores by way of their
angle of attack against the inclined thrust-plate 95. A side force
is created by the pistons 93 on the wall of each bore in those
bores subjected to pressurised fluid, causing rotation of the motor
cylinder-barrel 61 about its longitudinal or central axis for
rotation. The cylinder-barrel 61 in turn rotates shaft 106 and
mechanical power is transmitted through gears 120, 123, 130 to the
ring gear 131 of the differential. Bevel gearing of the
differential then determines the respective speeds of the axle
output shafts 7, 8 that drive the wheels of the vehicle.
DETAILED DESCRIPTION OF THE SECOND EMBODIMENT OF THE INVENTION
As the second embodiment differs in only one main respect from the
first embodiment, description is only necessary to show the main
points of differences. As the internal components are identical to
those described for the first embodiment, for convenience, most
that are here numbered will carry the same reference numeral as for
the first embodiment
Essentially as shown in FIGS. 5 to 9, the housing member 200
containing within the pairs of fluid passages 201, 203 and 202, 204
that are used in linking the pump to the motor, is attached to an
exterior junction surface (second parting-plane) shown as 210
provided on the upper surface of housing member 212. Housing
element 212 is provided with an opening 215 which acts as the
register for housing member 200 and where fastening screws 217 are
used to secure housing members 200, 212 together. Housing member
212 combine with the lower transaxle housing member 213 to form an
internal chamber 220.
Housing member 200 is provided with a face surface 221 for the
valve-plate of the pump, and on the downwards extending portion 205
is provided with face surface 222 for the valve-plate 34 of the
motor. Check-valves shown as 225 are included for each passages
203, 204 respectively, and plugs 226, 227 as shown in FIG. 9, are
used to close the ends of passages 201, 202. Plugs 226, 227 do not
need to be threaded in passages 201, 202 as they are prevented from
being expelled because of adjacent wall formed by the opening 215
in housing member 212.
This embodiment also contrasts with the first embodiment in that
substantially more cooling fins shown as 233 can be included on the
top surface 234 of housing member 200, thereby providing more
efficient and effective cooling of the fluid passing through
passages 201, 202, 203, 204 between the pump and motor.
Although the present invention will still allow some of the heat to
be transferred out from the transaxle by conduction through the
hydraulic fluid medium to the outer housing in a similar manner as
used in the prior art devices, the total cooling effect is enhanced
because the most important area to be cooled, namely the fluid path
between pump and motor, is directly adjacent that portion in the
housing on which the cooling fan is most effective. Consequently,
the hydrostatic transaxle tan be operated for longer periods at
rated loads with less risk of overheating the power transmission
fluid.
A control-shaft 251 is journalled at 252 in the housing member 200.
Having the control shaft located in the housing member containing
the internal fluid passages can also be performed in the first
embodiment of the invention if so desired.
Rotary vent valve 260 shown in FIGS. 7 to 10 may be used to
provided a "wider band neutral" effect for the hydrostatic
transmission, and as well as if desired, a "freewheel" or fluid
dumping effect. Essentially, the valve 260 is supported in bore 261
in housing member 200 and is provided with a fluid short-circuit
shown as small passage 263 which, when the swash-plate of the pump
is near its zero inclination angle, passage can connect with two
passages shown as 265, 266 in housing member 200 which are in
communication with fluid passages 201, 203 and 202, 204
respectively. As shown, any fluid released by the pump when the
swash-plate has a small inclination angle can divert through
passage 263 rather than flow to the hydraulic motor where it would
act in causing the motor assembly to rotate. FIG. 7 shows how valve
260 can be linked to control-shaft 251 by means of linkages 270,
271, 272 so that the movement in position of passage 263 occurs as
control-shaft 251 is moved by the operator of the vehicle. By
varying in the span or arm length of the linkages, it is possible
to obtain varying characteristics from the "wider band neutral" to
suit each particular application. Valve 260 is shown as the
left-hand illustration in FIG. 10 and shows hidden passage 269
which is perpendicular to passage 263. Disconnection of linkage 270
with valve 260 would allow the valve 260 to be rotated through
ninety degrees to provide a large flow short-circuit between
passages 265, 266 as hidden passage 269 becomes a short-circuit for
the fluid. Valve 280 shows a modification whereby grooves 281, 282
are provided for "O" ring type seals that surround passage 263.
Valve 290 illustrates a further modification where the valve can be
axially lifted so that passage 263 is no-longer in connection with
passages 265, 266 in housing member 200, so that in the lifted
position, slot 291 is open to passages 265, 266 to short-circuit
fluid into internal chamber 220. Thus the degree of flow
restriction caused by fluid having to pass through the restricted
passage 263 is overrided, and the vehicle can be easy pushed
without having to first start the engine. A further advantage of
having the vent valve in the housing element is that adjustments to
the operating condition of the hydrostatic transaxle can be made
without disassembly of the entire unit.
Although not shown or described in either of the embodiments of the
invention, a further modification falling with the scope of the
present invention would be to re-arrange lower housing member shown
as 3 in the area about the swash-plate 70 and bearing 72 so that a
fourth housing member could be used. The fourth housing member
would be provided with a hole for bearing 72 and a part-cylindrical
support-surface for the swash-plate 70. The fourth housing member
could be attached and secured to the inside interior wall of
housing element 3 or alternatively, be attached to the outside of
housing element 3 on a mounting face and arranged that part of it
extends through an openings provided the housing member 3. In this
manner, the housing member containing the fluid passages can
further be attached to the fourth housing element by means of stays
or studs which are arranged to pass through the top exterior to the
bottom exterior which would stiffen the complete housing structure
of the hydrostatic tranaxle.
Perhaps for certain applications, there may be advantage in
substituting the fixed-displacement axial piston swash-plate
hydraulic motor with that of another type. For instance, a
fixed-displacement external geared hydraulic motor could be used
instead and where the gears of the motor in this instance would be
journalled in bores provided in the same housing member containing
the fluid passages linking the pump to the motor.
A charge and/or power take-off auxiliary pump, preferably of the
gerotor internal gear type may also be disposed in the same housing
member that contains the fluid passages linking the pump to the
motor of the hydrostatic transmission. The gerotor pump being
driven by the input drive shaft and having fluid passages and
valves arranged in the same housing member to suit the needs of the
application. A further advantages in this arrangement would allow
the pressure setting of the gerotor pump to be adjusted easily as
the pressure relief-valve would have an external adjustment; the
fan cooling effect of the present invention would help keep the
fluid delivered by the gerotor pump to be kept as cool as possible;
all the external connections can be arranged to be near the top of
the transaxle thereby minimising the chances of being damaged.
In accordance with the patent statutes, we have described the
principles of construction and operation of our invention, and
while we have endeavoured to set forth the best embodiments
thereof, we desire to have it understood that obvious changes may
be made within the scope of the following claims without departing
from the spirit of our invention.
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